1. Field of the Invention
The present invention relates to a particle dispersion copper alloy in which particles are dispersed in a matrix composed of a copper alloy, and a method for producing the same.
2. Description of the Related Art
The combustion gas is produced in accordance with the reciprocating motion of a piston in a cylinder bore in an internal combustion engine of an automobile. A discharge port is provided for the internal combustion engine in order to discharge the combustion gas. The discharge port is opened/closed by a valve.
A valve seat is provided for the discharge port in order to seal the combustion gas. The valve, which makes the forward/backward movement in accordance with the opening/closing operation of the discharge port, makes sliding contact with the valve seat. Therefore, it is desired that the valve seat is excellent in the abrasion resistance.
A seat made of Fe-based sintered material or a seat made of copper-based self-fluxing alloy has been hitherto adopted as the valve seat. Such a valve seat is arranged for the cylinder bore as follows. In the case of the seat made of Fe-based sintered material, an annular member is manufactured, and forcibly introduced under the pressure. On the other hand, in the case of the seat made of copper-based self-fluxing alloy, cladding (or padding) is carried out in the vicinity of an opening of the cylinder bore.
In recent years, environmental protection has been highly concerned. Therefore, further clean gas discharge from the internal combustion engine and reduced fuel consumption ratio have been attempted. In accordance with such attempt, the ratio of fuel to the air is decreased when fuel is combusted in the internal combustion engine. In other words, the fuel becomes thinned. However, when the combustion method as described above is carried out, the known seats made of Fe-based sintered material or copper-based self-fluxing alloy are undesirably worn in a relatively short period of time.
In order to improve abrasion resistance of the seat made of the copper-based self-fluxing alloy, for example, it is preferable to disperse hard particles in the copper-based self-fluxing alloy. From this viewpoint, Japanese Laid-Open Patent Publication No. 2001-105177 suggests that a silicide having a three-dimensional Laves structure is dispersed as hard particles in a copper-based self-fluxing alloy.
In the case of this technique, the average particle diameter of the hard particles ranges over 50 to 200 μm. In the case of the particle-dispersed copper alloy containing the coarse particles as the hard particles as described above, the surface roughness is excessively increased. Frictional heat may undesirably be increased when the valve makes sliding contact.
On the other hand, Japanese Patent No. 3373076 and Japanese Laid-Open Patent Publication No. 2002-194462 disclose the fact that a silicide is crystallized or deposited from a component which constitutes a copper alloy, and provided as hard particles. However, in this case, because the hard particles may not be dispersed uniformly, it is difficult to uniformize abrasion resistance throughout the seat.